Balance filter comprising two acoustic wave filters connected to a single ground terminal
A balance filter includes two acoustic wave filters connected between a single unbalanced terminal and two balanced terminals, and a ground terminal connected to the two acoustic wave filters via a first interconnection portion and a second interconnection portion. The first interconnection portion is connected to the two acoustic wave filters, and the second interconnection portion is connected to the first interconnection portion in a region that is located between the two acoustic wave filters and extends in a direction orthogonal to a direction in which the two acoustic wave filters are aligned.
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This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-045583, filed on Feb. 27, 2008, the entire contents of which are incorporated herein by reference.
FIELDThe present invention relates to a balance filter having an unbalance-balance conversion function.
BACKGROUNDRecently, compact and light surface acoustic wave (SAW) filters have been used as filters in mobile communication devices in terms of downsizing, weight saving and frequency raising. It is now required to reduce the number of parts to achieve further improvements in downsizing and weight saving of the mobile communication devices and to realize a SAW filter having a new function. For example, a balance filter having an unbalance-balance conversion function (balun function) has been proposed. Balanced signals use a pair of signal lines and define data by the potential difference between the signal lines. The signals on the signal lines have an identical amplitude and a 180-degree phase difference. An unbalanced signal defines data by the potential of a single signal line to the ground potential.
Balance filters having the unbalance-balance conversion function are described in Japanese Laid-Open Patent Publication Nos. 2003-528523 (Document 1) and 2003-124777 (Document 2). The balance filter described in Document 1 has a plurality of ground terminals. The balance filter described in Document 2 has six electrode pads on a package. Thus, there is a difficulty in further downsizing of the balance filters. If only one ground terminal is used, the degree of balance will be degraded and the bandpass characteristic will be deteriorated.
SUMMARYThe present invention has been made in view of the above circumstances and provides a downsized SAW filter without degrading the degree of balance and deteriorating the bandpass characteristic.
According to an aspect of the present invention, there is provided a balance filter including: two acoustic wave filters connected between a single unbalanced terminal and two balanced terminals; and a ground terminal connected to the two acoustic wave filters via a first interconnection portion and a second interconnection portion, the first interconnection portion connected to the two acoustic wave filters, and the second interconnection portion connected to the first interconnection portion in a region that is located between the two acoustic wave filters and extends in a direction orthogonal to a direction in which the two acoustic wave filters are aligned.
First, a description will be given of a balance filter in accordance with a first comparative example.
A first interconnection portion 24 is connected to both the SAW filters 14a and 14b. Two ground terminals 26a and 26b are connected to the first interconnection portion 24, and the corresponding comb electrodes of the IDTs of the SAW filters 14a and 14b are grounded.
The first comparative example employs the two ground terminals 26a and 26b, as illustrated in
In the SAW filter 14a, three IDTs of IDT11, IDT12 and IDT13 are formed between a pair of reflection electrodes 30. One of the comb electrodes of IDT11 and one of the comb electrodes of IDT13 are connected to the balanced output terminal 18a, and the other comb electrodes are connected to the first interconnection portion 24. One of the comb electrodes of IDT12 is connected to the first SAW resonator 16, and the other is connected to the first interconnection portion 24. Similarly, in the SAW filter 14b, three IDTs of IDT21, IDT22 and IDT23 are formed between a pair of reflection electrodes 30. One of the comb electrodes of the IDT21 and one of the comb electrodes of IDT23 are connected to the balanced output terminal 18b, and the other electrodes are connected to the first interconnection portion 24. One of the comb electrodes of IDT22 is connected to the first SAW resonator 16 via the third interconnection portion 20, and the other is connected to the first interconnection portion 24. That is, the first interconnection portion 24 is connected to both the SAW filters 14a and 14b.
The first interconnection portion 24 is connected to a second interconnection portion 32 in a region X, which is located between the SAW filters 14a and 14b and extends in a direction orthogonal to the direction in which the SAW filters 14a and 14b are aligned. A single ground terminal 26 is connected to the second interconnection portion 32. That is, the ground terminal 26 is coupled to both the SAW filters 14a and 14b via the first interconnection portion 24 and the second interconnection portion 32. Thus, one of the comb electrodes of each of IDT11, IDT12 and IDT13 is grounded. Similarly, one of the comb electrodes of each of IDT21, IDT22 and IDT23 is grounded. The interconnection portion 24 has a pattern that is symmetrical about a center line A-A between the SAW filters 14a and 14b. Further, the balanced output terminals 18a and 18b are symmetrical with each other about the center line A-A.
In the first SAW resonator 16, a single IDT31 is provided between the two reflection electrodes 30. One of the comb electrodes of IDT31 is connected to the SAW filters 14a and 14b, and the other electrode is connected to the unbalanced input terminal 22.
Next, a description will be given of the structures of the SAW filters 14a and 14b and the first SAW resonator 16. In the following, the number of pairs of electrode fingers is defined so that one pair consists of one finger of one of two comb electrodes of one IDT and one finger of the other comb electrode of the IDT, these electrode fingers being adjacent to each other and interleaved. An aperture length is the length of a section in which two adjacent, interleaved electrode fingers laterally overlap with each other. In
As illustrated in
In contrast, as illustrated in
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As illustrated in
In the first embodiment, the two SAW filters 14a and 14b are respectively double-mode SAW filters. Thus, as illustrated in
The balance filter of the first embodiment may have a wafer level package (WLP) structure, as illustrated in
The present invention is not limited to the structure of the first embodiment illustrated in
As illustrated in
As illustrated in
The balance filter of the second embodiment has only one ground terminal 26, so that downsizing of the balance filter can be realized.
Third EmbodimentAs depicted in
When the anti-resonance frequencies of the second SAW resonators 46a and 46b are set at frequencies close to the pass band and outside thereof, it is possible to form an attenuation pole close to and outside of the pass band. It is thus possible to increase the attenuation outside of the pass band without increasing the insertion loss.
Further, the balance filter 10 of the third embodiment can be miniaturized because only one ground terminal 26 is employed like the first embodiment.
Fourth EmbodimentAccording to the fourth embodiment, like the first embodiment, the first interconnection portion 24 and the second interconnection portion 32 are connected to each other in the region X that is located between the SAW filters 14a and 14b and extends in the direction orthogonal to the direction in which the SAW filters 14a and 14b are aligned. Thus, as in the case of the first embodiment, the parasitic capacitances and the parasitic inductances coupled to the balanced output terminals 18a and 18b can be equalized in the arrangement in which the second SAW resonators 16a and 16b are provided between the SAW filters 14a and 14b and the balanced output terminals 18a and 18b and are connected in series to the SAW filters 14a and 14b. Thus, the fourth embodiment is capable of improving the amplitude balance and the phase balance that depend on the frequency and the bandpass characteristic. Particularly, increased attenuation resulting from the amplitude balance with respect to the frequency can be realized at frequencies outside of the pass band.
When the anti-resonance frequencies of the first SAW resonators 16a and 16b are set at frequencies close to the pass band and outside thereof, it is possible to form the attenuation pole close to and outside of the pass band. It is thus possible to increase the attenuation outside of the pass band without increasing the insertion loss.
Further, the balance filter 10 of the fourth embodiment can be miniaturized because only one ground terminal 26 is provided like the first embodiment.
Fifth EmbodimentIn the fifth embodiment, like the first embodiment, the first interconnection portion 24 and the second interconnection portion 32 are connected to each other in the region X that is located between the SAW filters 14a and 14b and extends in the direction orthogonal to the direction in which the SAW filters 14a and 14b are aligned. The second SAW resonators 46a and 46b connected in series to the SAW filters 14a and 14b are provided between the SAW filters 14a and 14b and the balanced output terminals 18a and 18b. The fifth embodiment is capable of improving the amplitude balance and the phase balance that depend on the frequency and the bandpass characteristic. Particularly, increased attenuation resulting from the amplitude balance with respect to the frequency can be realized at frequencies outside of the pass band.
When the anti-resonance frequencies of the second SAW resonators 46a and 46b and the first SAW resonators 16a and 16b are set at frequencies close to the pass band and outside thereof, it is possible to form the attenuation pole close to and outside of the pass band. It is thus possible to increase the attenuation outside of the pass band without increasing the insertion loss.
Further, the balance filter 10 of the fifth embodiment can be miniaturized because only one ground terminal 26 is provided like the first embodiment.
The first through fifth embodiments employs the double-mode SAW filters for the SAW filters 14a and 14b. However, the present invention is not limited to the double-mode filters but may use multi-mode filters in which multiple groups 28 of IDTs are aligned in the direction of SAW propagation. The SAW filters 14a and 14b may be replaced by boundary acoustic wave filters or other types of acoustic wave filters. These variations are capable of improving the amplitude balance and the phase balance that depend on the frequency and the bandpass characteristic, as in the case of the above-mentioned embodiments. The present invention includes a variation in which the input terminals are balanced terminals and the output terminal is an unbalanced terminal.
The present invention is not limited to the specifically disclosed embodiments, but include other embodiments and variations without departing from the scope of the present invention.
Claims
1. A balance filter comprising:
- two acoustic wave filters connected between a single unbalanced terminal and two balanced terminals;
- a single ground terminal connected to the two acoustic wave filters via a first interconnection portion and a second interconnection portion and arranged at a same side where the single unbalanced terminal is provided with respect to the two acoustic wave filters, the first interconnection portion connected to the two acoustic wave filters, and
- the second interconnection portion connected to the first interconnection portion in a region that is located between the two acoustic wave filters and extends in a direction orthogonal to a direction in which the two acoustic wave filters are aligned.
2. The balance filter according to claim 1, wherein the first interconnection portion is symmetrical about a line between the two acoustic wave filters.
3. The balance filter according to claim 1, wherein the two balanced terminals are symmetrical about a line between the two acoustic wave filters.
4. The balance filter according to claim 1, further comprising a first resonator that is provided between the two acoustic wave filters and the unbalanced terminal and is connected in series to the two acoustic wave filters.
5. The balance filter according to claim 1, further comprising a first resonator that is provided between one of the two acoustic wave filters and the unbalanced terminal and is connected in series to said one of the two acoustic wave filters and another first resonator that is provided between the other acoustic wave filter and the unbalanced terminal and is connected in series to the other acoustic wave filter.
6. The balance filter according to claim 1, further comprising a second resonator that is provided between one of the two acoustic wave filters and one of the two balanced terminals and is connected in series to said one of the two acoustic wave filters, and another second resonator that is provided between the other acoustic wave filter and the other balanced terminal and is connected in series to the other acoustic wave filter.
7. The balance filter according to claim 1, wherein:
- the two acoustic wave filters are multi-mode filters;
- the first interconnection portion has portions connected to the two acoustic wave filters on both sides of each of the two acoustic wave filters; and
- the portions of the first interconnection portion are connected to each other between the two acoustic wave filters.
8. The balance filter according to claim 1, further comprising:
- a third interconnection portion that connects the two acoustic wave filters to the single unbalanced terminal and the two balanced terminals;
- a piezoelectric substrate on which the two acoustic wave filters, the second interconnection portion and the third interconnection portion are formed; and
- a bump that is used for flip-chip mounting and is provided on the second interconnection portion and the third interconnection portion.
9. The balance filter according to claim 1, further comprising a third interconnection portion that connects the two acoustic wave filters to the two balanced terminals; wherein:
- the two acoustic wave filters are multi-mode filters and have multiple interdigital transducers;
- the third interconnection portion is connected to more than two interdigital transducers of the multiple interdigital transducers; and
- the first interconnection portion is arranged so as to surround the two acoustic wave filters and crosses the third interconnection portion that is connected to the more than two interdigital transducers.
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Type: Grant
Filed: Feb 25, 2009
Date of Patent: Nov 22, 2011
Patent Publication Number: 20090261921
Assignee: Taiyo Yuden Co., Ltd. (Tokyo)
Inventors: Akira Moriya (Yokohama), Yasufumi Kaneda (Yokohama), Osamu Kawachi (Yokohama)
Primary Examiner: Barbara Summons
Attorney: Arent Fox LLP
Application Number: 12/392,622
International Classification: H03H 9/64 (20060101);